1. Field of the Invention
The present invention relates to a developing apparatus which is adapted to be used for a copying machine or a printer employing an electrophotographic technique.
2. Description of the Related Art
The inventors of the present invention know that there is a developing apparatus which includes a developing bath, a toner feeding bath, and a partition plate provided between the developing bath and the toner feeding bath. The developing bath is located closer to a photoconductor provided in a copying machine, and the toner feeding bath stores magnetic toner for feeding it to the developing bath. The partition plate provides a toner outlet for communicating the developing bath with the toner feeding bath.
The developing bath provides a developing roller rotationally supported on the developing apparatus itself and a doctor for restricting an amount of developing powder (toner and carrier) attracted on the developing roller. The developing roller has a sleeve and a magnet located inside of the sleeve, the sleeve serving to rotate in an opposite direction to the rotation of the photoconductor and the magnet serving to rotate in an opposite direction to the sleeve.
The toner feeding bath provides a toner stirring roller for stirring magnetic toner and feeding the magnetic toner into the developing bath through the toner outlet.
In operation, the developing powder stored in the developing bath is conveyed for development to the photoconductor provided in the copying machine through the effect of the rotations of the sleeve and the magnet provided in the developing roller as the amount of the developing powder attracted on the sleeve is restricted by the doctor.
Since the magnet is not long enough to reach both ends of the developing roller, the magnetic attraction is so weak at the end portions of the developing roller that the developing powder is thrown off the developing roller through the effect of the developing roller itself, resulting in causing leakage of the developing powder from both end portions of the developing roller.
In order to block the leakage, there is also provided a block portion for preventing the developing powder from being leaked out as well as a sealing material made of suede located between the developing roller and the block portion and the bottom wall of the developing bath in a manner to allow the sealing material to come in contact with the surface of the developing roller.
The above-mentioned developing apparatus will be described with reference to FIGS. 1 to 4 in the followings.
In FIG. 1, a photoconductor 11 provided in a copying machine is shown. The developing apparatus having a developing bath 12 is so arranged that magnetic toner 13 is stored in a toner feeding bath 14 and a partition plate 15 is provided between the developing bath 12 and the toner feeding bath 14.
The developing bath 12 is located closer to a photoconductor 11, and the toner feeding bath 14 feeds magnetic toner 13 stored therein to the developing bath 12. The partition plate 14 provides a toner outlet 16 for communicating the developing bath 12 with the toner feeding bath 14.
The developing bath 12 provides a developing roller 18 rotationally supported on the developing apparatus itself and a doctor 20 for restricting the amount of developing powder (toner and carrier) 19 attracted on the developing roller 18.
As shown in FIG. 2, the developing roller 12 has a sleeve 21 and a magnet 22 located inside of the sleeve 21. The sleeve 21 serves to rotate in an opposite direction with respect to a rotation of the photoconductor 11 and the magnet 22 serves to rotate in an opposite direction with respect to a rotation of the sleeve 21.
The toner feeding bath 14 provides a toner stirring roller 23 for stirring magnetic toner 13 and feeding the magnetic toner 13 into the developing bath 12 through the toner outlet 16.
In operation, the developing powder 19 stored in the developing bath 12 is conveyed for a development to the photoconductor 11 provided in the copying machine through the effect of the rotations of the sleeve 21 and the magnet 22 provided in the developing roller 18 as the amount of the developing powder attracted on the sleeve 21 is being restricted by the doctor 20.
Since the magnet 22 is not long enough to reach both ends of the developing roller 18, the magnetic attraction is so weak at the end portions of the developing roller 18 that the developing powder 19 is thrown off the developing roller 18 through the effect of the developing roller 18 itself, and it results in causing a leakage of the developing powder 19 from both end portions of the developing roller 18.
In order to block the leakage of the developing powder 19 as shown in FIGS. 3 and 4, there is also provided a block portion 24 for preventing the developing powder 19 from being leaked out as well as a sealing material 25 made of suede located between the developing roller 18 and the block portion 24 and the bottom wall of the developing bath 12 in a manner to allow the sealing material 25 to contact with the surface of the developing roller 18.
However, the suede-made sealing material 25 has the following disadvantages. It may provide variable pressure on the developing roller 18 and its woolen surface may be stripped off as a result of long-time rotation of the developing roller 18. These disadvantages result in making the sealing effect unstable, thereby causing a leakage of the toner out of both end portions of the developing roller 18. That is, the toner is spilt out of the developing apparatus.
Further, since the split toner is circulated on the powder-laminated surface of the developing roller 18, a fog phenomenon may take place on the edges of the resulting image.
In the above-mentioned developing apparatus, when the toner on the sleeve 21 meets the sealing member, that is, the obstacle to the circumferential movement of the sleeve 21, the longitudinal rotation (perpendicular to the circumferential direction) is applied to the circumferential rotation of the toner, resulting in moving the toner in the longitudinal direction and thereby leaking the toner out of the ends of the developing roller 18.